Measuring Type
Some Definitions
Type measurements have not gone metric. They actually haven't even gone English. The terminology is obscure, the measurements can shift, and the whole thing seems at first horribly archaic. Get over it. It’s not that hard, and it makes you look like you know what you are doing, using that nomenclature. So, to start, here’s some definitions.
Baseline
This is the line that the bottom of lowercase letterforms rest on, or more precisely, non-curved letterforms. Letterforms with curves at the bottom often drop below the baseline so that they optically align.
Points
The basic unit in measuring type is the point, which is about 1/72nd of an inch. For the sake of not entirely losing our minds, we will forever after use the PostScript point, which is 1/72nd of an inch.
Points are mostly used to measure verticals. So, you use points to measure type height and leading. The measurement is from the top of the ascenders to the bottom of the descenders, with a bit of spacing thrown in, mostly to confuse the uninitiated. When speccing, or specifying type, one states the typeface height and the leading, in points, such as Helvetica 12/14 or Garamond 16/24.
Myriad (left) and Adobe Garamond, both at 60pt. The red rectangle is 60pt tall.
Picas
A pica is 12 points. There are 6 picas to an inch (Hey! do the math…). The pica is used for horizontal measure, most often for line or column width. It may also be used for vertical measure, when talking about column height.
Leading
Leading (pronounced ledding) is the vertical space between lines of text. The basic rule of thumb is to set leading at around 120% of the point size of the text.
Em and Ens
An em space is a square measure equal to the height of a given typeface, so if you have 12pt type, your em is 12pt by 12pt. Ens are half an em. Both of these are called quads when using metal type, and were used for word spacing. The illustration below shows different quads and their corresponding word spacing percentages as used in Adobe InDesign.
Quads, from top to bottom: em, en, 1/3 em, 1/4 em, 1/5 em, 1/6 em. The percentage is from word spacing settings in the justification section of a paragraph style in Adobe InDesign.
Since ems are mutable, that is, they change with the type size, they are used for line spacing (leading), paragraph indents, and anywhere else a proportional unit of measure might come in handy.
